text:
Does P-Factor increase with thrust?
I was trying flightgear simulator since I am not a pilot (but have completed ground school) and one thing I have noticed is that the P-Factor increases with thrust applied whether taking off or in cruise flight.
Is this realistic? Does P-Factor vary based on thrust?

Yes, it should. In the end, p-factor is just a funny word for the out-of-center shift of the thrust vector, and if the vector is larger, the effect should be equally larger.

YES! In fact P -Factor is the asymmetric thrust that the propellers generate at increased AoA(Angles Of Attack). In other words P-factor is the asymmetric disk loading.
Thrust and P-factor
For the majority of single engine aircraft, this  means that the aircraft will yaw to the left at high angles of attack unless an appropriate right rudder alteration is applied.


text:
Why are contrails not visible from the cabin?
If you observe a plane flying whilst on the ground, plenty of times you will see contrails:

Why are they not visible from the plane itself when sitting in the most rear part of the cabin even by trying to look towards the rear of the plane fuselage? They seem to be quite close to the engines.
Knowing that they form due to the heat, they should be seen quite close to the engine.

The cobtrails is created by water moisture from the engine and moisture takes times to cool down to be visible

Next time you see a contrail being formed, grab a pair of binoculars and and take a close look. You'll see that there's quite a distance between the tail of the airplane and the contrail.

Even in the photo in the question, you can clearly see that the contrail begins some distance behind the plane.

Contrails do not form due to heat, but in fact the opposite: cold.
They occurs when water from fuel combustion exceeds the saturation point of the ambient air. As it is unable to hold more water it turns into water vapor instead. This freezes at sub-zero temperatures into ice crystals and you end up essentially making a cloud.
Since the saturation point is connected to temperature (think mixing sugar in cold vs. hot water) this happens a bit back from the fuselage when the exhaust cools down. The point where this happens is dependent on the outside temperature and the existing humidity.
Under the correct conditions you can see contrails from the cabin, but usually they crystallize too far back to be seen. See this and this video for it occurring.

Would it necessarily be ice crystals and not water droplets? Steam from a kitchen kettle condenses into visible water droplets. Would water vapor from an engine exhaust never pass through a condition under which it could condense without already being below freezing point?

Either it's water droplets or ice crystals. Water crystals are impossible.

@AnthonyX My brain switched off there for a bit, you are of course right.

Water ice crystals.

Not the terms I would use.  Out of the engine it is water vapor.  Once it precipitates out (exceeds the saturation limit of the air) then is it liquid water.  Once it is cooled below freezing it is ice.   A cloud can be tiny water droplets or ice.  They small enough they are held in suspension.

The distance between the engine and the start of the contrail depends on:

the engine type
the temperature of the outside air
the moisture content of the outside air.

Usually the contrails don't form before the tail of the aircraft, but in extreme cold or humid air contrails can be seen forming just behind the wing.
On larger aircraft you have a better change of seeing the contrail from inside the aircraft. On the 747 you can often spot them for the window of the rear passenger door.

The last photo illustrates an additional factor: The visibility increases significantly if the contrails are lit almost exactly from behind. From far away and with the sun almost exactly behind the aircaft, heat refraction alone may be enough to show a contrail.

This is more a comment than an answer, but since I have a picture, I write it as answer.
It has alredy been written that contrails may form aside or behind an aircraft, so you may or may not be able to see them from the rearmost seats.
But also note that the blast stream can be much lower than what you would expect. In a two-engine aircraft, you have to look down from the upper edge of the window, and even then, the stream will be on the lower border of your field of view. Of course, the stream of the outer engines of four-engine aircrafts will be more centered in your field of view.
If you are flying over a scenery with high optical contrast, you can recognize the blast as a sharply defined region where the view is very blurry, as in the lower right region on this picture:

This was taken from the last seat row of a A340 after takeoff at Chicago O'Hare, and you can see the blast of the outer engine. (And yes, the outer stabilizer is in a little weird condition...)
So, look out for these blurry regions, that's where contrails may form.

EDIT: (just for fun)
Coming home from vacation yesterday, I noticed another sign for contrails from your aircraft: The contrail's shadow:

Unfortunately, the clouds became less dense when I made the photo, before I could also see a good shadow of the aircraft itself.

Sorry for the OT. Is this actually an A340 or an A330? Seems the latter from the wing.

Definitively A340, as it had 4 engines. The picture is zoomed. And if it were a 2-engine A330, I had to make the poto pointing more downwards to get the blast on the picture.

darn wings, always getting in the way of great pictures...

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text:
How dangerous is airborne debris?
I live next to HTDA Julius Nyerere International Airport and I do occasionally see Airborne debris, mostly plastic bags flying around at 1000 or more feet.
How dangerous can this be?

The FAA's advisory circular on Airport Foreign Object Debris (FOD) Managament mentions plastic bags and other trash as a type of FOD and says these are the dangers:

FOD Hazards.   FOD can severely injure airport or  air carrier personnel or damage  equipment.  Types of potential damage include: cutting aircraft tires; being  ingested into engines;  or becoming
  lodged in mechanisms affecting flight  operations.  Personnel injuries
  or even death  can occur when jet blast propels FOD through the
  airport environment at high velocities.

Since you're asking specifically about airborne items, that would mean the most likely dangers from that list are engine ingestion or "becoming lodged in mechanisms affecting flight operations".
The main issue with a plastic bag seems to be that it damages the engine, rather than stopping it entirely. This paper recommends an inspection if any "soft material" (including plastic bags) are ingested:

Remains on impellers and/or LP diffuser exit ducts confirm a bird or soft material has passed through the Engine and possibly
  contaminated the secondary air system, fuel nozzle and HP turbine vane
  cooling air passages.
If contamination occurs, hot section components deteriorate rapidly, increasing the cost of refurbishment. Therefore, operators are
  recommended to carry out a hot section inspection (HSI) as soon as
  possible after a bird strike or ingestion of soft material is
  confirmed

As for affecting flight instruments, the main danger is probably that the bag covers the pitot tube, resulting in false airspeed readings. That can be catastrophic if the pilots don't realize what's going on, but many larger aircraft have multiple pitot tubes so it would probably need a lot of plastic bags (or a lot of bad luck) to cause an accident. And a bag stuck on the windscreen could block a pilot's view but if there are two pilots then that shouldn't be critical.
Of course, all of the above applies to airliners. If you fly a light piston single through airborne debris the results could be worse because of the lack of technical (and perhaps crew) redundancy.

With a light piston single, though, you don't really have to worry about the bag being ingested into the engine and it would get shredded by the prop before it would have a chance to get stuck on the windshield. Blocking the pitot tube would certainly still be unhelpful, but, when operating that close to the field, light aircraft will usually have the ground in sight and can be flown without the instruments if needed.

@reirab there's a (small) chance that a plastic bag that gets past the propeller could get blown into the engine cooling inlets (where it would probably melt and smell awful, and might start to smoke). It  also has a (small) chance of blocking the engine air intake, which can choke out the engine.  I can't recall reading about either of those in an accident report's Probable Cause though :)

@voretaq7 True, but that would take one serious plastic bag to survive an encounter with a prop. Kevlar bag, maybe?

@reirab: The bag can be simply lucky and miss the blades. At 80 knots the plane moves about 1 m during the time it takes a prop at 2400 rpm to make a complete revolution. With 4 blades, it still leaves 25 cm between the blades and that's enough space for noticeable piece of plastic to get through.

I would say not much. Aircraft are designed to survive collision with small bird and plastic bags are lighter than that. A plastic bag probably won't even visibly damage the skin and if ingested in an engine, it will burn quickly and likely without noticeable impact on the engine performance. The only issue I can think of is if it gets stuck on some important sensor.
There has been an incident where aircraft collided with some kind of banner hanging from a hot air balloon which clogged pitot tubes and caused airspeed indicators, and auto-flight systems that need them, to fail.
Unreliable airspeed should not be a big deal with proper crew training, but the way that crew mismanaged the situation shows there is some risk. However plastic bags are smaller than the banner in that incident, so the chance of one hitting one of the three critical spots on the aircraft is quite low.

Not all aircraft are rated for bird strikes.

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text:
Are airliner flight plans/routes preset?
KLM has 3 flights daily from BLQ to AMS.
How do all of the crews handle the flight plans? Do the make a plan for every flight every day or do they have a database in which preset and stored flight plans are available and are ready to be extracted?

Airlines have an own department that is solely responsible for their flights and flight plans: Dispatch. Since single airways can have different availability or just direction for different days or even times of the day, there will be a preset pool of routes for recurring flights, which can then be adapted for anything out of the ordinary, like NOTAMS, weather forecasts, operational requirements like airspace closure, etc...
The flight plan is usually submitted by the dispatchers and not the aircrew.

Most airlines will have predefined plans, which can be modified as needed (for example when there are NOTAMs).
And newer aircraft may even have a standard list of plans preprogrammed in their FMCs, again modifiable of course.

They are called company routes. They are customised for an airline and added to a section of the monthly Navigation Database the FMS manufacturer sells to each airline. Flight plans can also be uplinked by the airline operation center to the FMS. Both of these the pilot can select into the active/primary flight plan.


text:
What is the lifespan of an airline engine?
As per subject, what is the lifespan of a jet engine? Do they have a fixed hours which they can be used and regardless of the state have to be exchanged or are they serviced and maintained until they are deemed not good for use?
If they do have a lifespan, I suppose also that different types of airliner engines and models will have different lifespans.

In general, the engine life is measured in terms of two things:

Flight hours
Flight cycles

A takeoff and a landing counts as a flight cycle.
The most important concept in engine life is the Time Between Overhaul(TBO), which is basically the manufacturer recommended time period after which the engine is stripped down,checked thoroughly and required parts replaced. After overhaul, the engine is usually cleared till the next TBO.
An overhauled engine is theoretically as good as a new one and comes with the same life (TBO) and warranty, if applicable. Airline engines (for example the Rolls Royce Trent series) usually have TBOs of over 15000 hours. The record for maximum time for an engine on wing (i.e. use in aircraft before removal for overhaul) is well over 40,000 hours.
The life of an engine is given by the manufacturer and are different for different engines. However, the engine life depends on a number of parameters and is usually different for various engine components.

The rotating components have life limits which are less than the engine and are replaced periodically, mostly during the TBO.
For example, the turbine blades are replaced after a set number of turbine cycles and/or after a set number of hours, which are lesser than the others.
In addition, most rotating components (compressors, turbines) are periodically subjected to checks, and are replaced if found damaged.
In case of abnormal operations, some parts are required to be replaced. For example, if one engine is required to give excessive thrust (for example in case of One Engine Inoperative), the engine is subjected to thorough checks similar to TBO.

Airline engines are usually serviced (Overhauled at TBOs) and maintained till they are deemed not good to use or not economical to (service/repair and) operate anymore.
Most of the engine manufacturers employ condition based health monitoring programs, which helps them to plan when to service and repair the engine. As a result, the engine life varies based on its condition.

What about hours it just spends on the wing without flying? If airplane is parked somewhere for ten years whats has to be done with the engines?

There are a few other things in the abnormal category that can shorten the life of a turbine engine (e.g. "hot starts"), and the "hot section" components usually have their own timelines for inspection or replacement (which may coincide with the compressors and such for convenience, but don't have to - particularly if the hot section's inspection comes up sooner from abnormal ops)

Any info on this 40,000 hour engine? That sounds interesting.

@FreeMan It was a Rolls Royce RB211-535E4 on a Boeing 757

Cool, thanks! Sounds like it's a regular thing for the RB211, not one particular engine that set a record.

@FreeMan It was for a particular engine. The average time to visit shop is around 20000 hours.


text:
When does a flight require a copilot?
I was wondering if there are regulations for when a flight requires both a pilot and copilot.
I always assumed a copilot is required once civilian passengers are aboard, but when I recently was a passenger in South-African and South-American sight seeing flights, the pilot was always flying alone. Flights in europe however always had a pilot and copilot.
Is this regulated by laws or can the pilot / airline company decide it on their own?

The difference you noted likely had to do with the size of the aircraft involved. Even in the U.S., there are some small aircraft in airline operation with only one pilot. These aircraft are very small for airline operations, though, such as the Cessna 208 Caravan. Most airline transport aircraft are much larger than this and are multi-crew.

A flight requires pilot & copilot when the aircraft being flown requires it.
A multi-crew aeroplane is one that requires a flight crew of at least two pilots. One of them is the pilot-in-command (the captain) and the other is the co-pilot (or first officer). All jet air transport aeroplanes and the vast majority of turbine powered air transport aircraft and business jet are multi-crew aeroplanes.
The definition in Annex 1 — Personnel Licensing states that it is: "an aircraft required to be operated with a co-pilot as specified in the flight manual or by the air operator certificate."
So the secondary answer is no, it cannot be decided by a pilot or an operator, it is a statutory requirement.

Annex 1 of what?

@Trengot - good point, I thought I had linked that part. I must have forgotten.

bah, and thanks to @JanHudec for fixing my awful linking ability. sigh

There is more to be answered here: There are rules which aircraft may be certified for single pilot operations and which may only be certified for multi-crew operation.

Yes, I agree. I was having trouble finding that so I put what I knew so far with the hope someone else could provide more info or I may have more time later. Didnt expect to be accepted answer so fast.

Also, you may sometimes also see the term "Second-in-Command" used for the FO. IIRC, SIC is the official term for the position in U.S. regulations, for example.

Soooo When does an aircraft must specify a crew of >1 to obtain certification?

This answer is incorrect at multiple levels, for the US at least. First of all, it is controlled by regulation, not by law, so it is not "statutory". FAA regulations are not laws (thank god we don't live in a dictatorship... yet). Secondly, the answer does not clearly identify the situations involved.

@TylerDurden there is a world outside the US. I linked to the ICAO information on this matter. I see youve posted another answer with more or less the same premise as my very first sentence. So I fail to see how "This answer is wrong at multiple levels"

There is no regulation to cover minimum crew when flying privately, other than as required by the airplane manual.
For commercial flights it gets a bit more complicated and the answer is, well, "it depends".
In EASA comercial flying the minimum crew compositon is defined here:
EU OPS (965) Subpart N
Ops 1.940 Composition of flight crew

(b) Minimum flight crew for operations under IFR or at night. For operations under IFR or at night, an operator shall ensure that:

for all turbo-propeller aeroplanes with a maximum approved passenger seating configuration of more than nine and for all turbo-jet aeroplanes, the minimum flight crew is two pilots; or

aeroplanes other than those covered by subparagraph (b)1 above are operated by a single pilot provided that the requirements of Appendix 2 to OPS 1.940 are satisfied. If the requirements of Appendix 2 are not satisfied, the minimum flight crew is two pilots.

And then the much longer Appendix 2 stating:

(a) Aeroplanes referred to in OPS 1.940(b)2 may be operated by a single pilot under IFR or at night when the following requirements are satisfied:

the operator shall include in the Operations Manual a pilot's conversion and recurrent training programme which includes the additional requirements for a single pilot operation;

in particular, the cockpit procedures must include:

(i) engine management and emergency handling;
(ii) use of normal, abnormal and emergency checklist;
(iii) ATC communication;
(iv) departure and approach procedures;
(v) autopilot management; and
(vi) use of simplified in-flight documentation;

the recurrent checks required by OPS 1.965 shall be performed in the single-pilot role on the type or class of aeroplane in an environment representative of the operation;

the pilot shall have a minimum of 50 hours flight time on the specific type or class of aeroplane under IFR of which 10 hours is as commander; and

the minimum required recent experience for a pilot engaged in a single-pilot operation under IFR or at night shall be 5 IFR flights, including three instrument approaches, carried out during the preceding 90 days on the type or class of aeroplane in the single-pilot role. This requirement may be replaced by an IFR instrument approach check on the type or class of aeroplane

(text is copy-pasted since getting a working link to a consolidated version of EU-OPS is a pain)

In the United States there are 3 basic situations that generally lead to an aircraft being flow by 2 (or more) crew:

The aircraft is categorized in the "air transport" class (eg commercial jets)
The maximum takeoff weight of the aircraft exceeds 12,500 pounds
The aircraft is so complex that the manufacturer recommends that it be flown by two pilots

Note that some aircraft, like variants of the 747, require 3 people because there is a station for an engineer.
In the old days the FAA used to require jets to be flown by two people, but now if a jet can come in under 12,000 pounds they can get certified for solo flight. There are a bunch of planes right now pegged at 12,500 and multiple manufacturers would like to go over that limit and still have them certified for solo flight, so there is some pressure on the FAA to relax the limit.


text:
What causes this surface texture, and how does it affect flight characteristics?
The picture on this answer to "What is this plane seen in Mobile, Alabama?" shows a B-52D Stratofortress with a very irregular surface texture.
(Source)
Were they like this when they were new, or is it just because this is an old aircraft that serves as a display piece? Would a surface like this cause issues with airworthiness?

I believe this is buckling of the fuselage, due to heavy compression loading.
Buckling is the process of out-of-stress-plane movement which happens under compression. The below image shows it well.

Source
More info on buckling here.
Here's another picture, possibly of the same (type of) aircraft, with the description saying:

It appears that the fuselage contains a very heavy cargo, the weight of
  which is reacted by significant overall shear loading at the axial
  station of the landing gear. The overall shear loading is absorbed by
  the skin of the fuselage, which has developed significant
  post-local-buckling diagonal tension between internal ribs and
  stringers.

This seems plausible to me, it could be that upon a rough landing, there was excessive compressional loading exerted by the landing gear, which caused the buckling.
I'm not an expert on airworthiness, but usually buckling indicates that a part is loaded more than it's supposed to be.

Source
Other aircraft have it too, see  this question with a further explanation about buckling.


text:
Do carrier-less militaries maintain carrier qualifications on allied boats?
"How do jet fighters get to war?" made me wonder if there was any cross-training for carrier operations between allied nations. While the equipment could be different (see "Do carrier-less militaries retain the equipment for carrier operations?"), do nations that don't operate carriers have pilots with training on it?
For example, are any Australian pilots qualified to land an F/A-18E/F on an American carrier, even if their own plane can't do it?
Example of use would be in an emergency, i.e., land their F/A-18's on a US carrier even though they won't be able to takeoff, and the aircraft will likely need to be shipped.

@KorvinStarmast https://aviation.stackexchange.com/questions/38080/do-carrier-less-militaries-retain-the-equipment-for-carrier-operations

I would just like you to note that most air forces without carriers that purchase CV-capable fighters would almost undoubtedly acquire non-naval versions (hook, structural support and all cost quite a sacrifice in weight!) and thus their pilots would probably not find themselves in such a situation anyways. Case in point; many of the Level 1, 2 and 3 countries in the JSF program that don't posses carriers in their navy or are purchasing F-35's for their Air Forces would probably opt for the A and B variants. Just my two cents, hope this opened your perspective a little ;)

The problem with the carrier landing is currency and recency of experience

Example of use would be in an emergency, i.e., land their F/A-18's on
  a US carrier even though they won't be able to takeoff, and the
  aircraft will likely need to be shipped.

The approach to landing on a carrier is a specific technique, wherein an angle-of-attack approach is flown all the way to the deck(and a very firm landing) with the intent of landing on the centerline and catching the 3-wire.  An acceptable approach catches any of the wires (there are 4).  The counter intuitive(for someone not trained in CV landings) advance-throttles-to-full- power-upon-landing ensures that if the wires are missed (Bolter!) one goes around and tries again if there's enough gas.

An approach to an airfield typically does not entail this, but instead includes a higher speed approach, and a flare which reduces the impact force on the aircraft (but of course requires a lot more runway).
If the pilot of the F-18 has never had the initial qualification on a carrier(which takes hundreds of field landings and a Carrier Qualification flight), making that approach becomes a non-trivial exercise in risk assessment.
If you aren't trained for it, why are you doing it?

Is the captain of the ship willing to risk a mistake that will damage dozens of aircraft on the deck and perhaps kill a few people?
Is the pilot willing to risk the approach that he or she is
untrained for, with the known lethality of failed attempts?
The severity of failure can be seen in youtube videos of ramp strikes on carrier approaches.  I suppose the pilot could ask, but the Captain of the Ship and his Air Boss might refuse permission.  See risk analysis above.  During a shooting war ... who knows what people might try?
Here's an A-7 ramp strike that's a vivid example.

To demonstrate the complexity of the matter:
The USN requires both an initial qualification and currency in order for its pilots, who land on carriers as a matter of standard operating procedures, to do a certain number of landings per quarter/per year/etc in order to remain current. If you aren't current you have to get recurrent to land on the Carrier.
But what if that pilot had a PEP tour?
The US and Australia, among other navies, have a "Pilot Exchange Program" where we trade officers who fly in our services.  Part of building alliance relationship.  So, if this Australian pilot had done a PEP tour in USN hornets, and been a carrier qualified pilot, he may not be recent or current, but he knows the basics of how to fly a successful approach.  It's still a risk assessment issue since the Captain of the Ship, his Air Boss, and this pilot know that he isn't current, and that his kit may be out of configuration compared to USN hornets, so that he's flying a degraded or visual only approach.
He can ask, but a decision to try it will take the safety of the pilot, his aircraft, and everyone/everything on that carrier's deck into consideration first.  (Low probability, but on a given day, who knows?)

Here is an interesting story I am sure you will enjoy. It is about becoming qualified on aircraft carriers of our allies. I was attached to Attack-Squadron 86 flying A7-E's in the mid-1980's off the USS Nimitz. Accumulated a little over 300 traps with around 100 of those at night. One trap was VFR during the day in a rainstorm, and I never saw the ship once passing the 45. No needles, no radar, and just my head in the cockpit on instruments flying an instrument approach to touchdown plus/minus 3 feet at the trap. But that is another story.
There was a gentleman in our squadron whose call sign was Bagrat. He was a US Navy Commander. Now he got the call sign for bagging traps. And he was good. We were graded on every trap. There was a No Grade, a Fair, an Okay, and an Okay underlined (perfect). These grades were averaged for a pilot over the period that the ship was at sea and then awards handed out for the top grades. I don't remember Bagrat being in the top much, but there was one thing that was certain, he always got aboard and it was either a Fair or Okay.
The LSOs often had words with him on the debrief. "Hey Bagrat were you spotting the deck again!?" Spotting the deck was a term we used to refer to the fact that the approach was not flown using the optical system (the ball), but by looking at the deck. Not many pilots could consistently land an aircraft without scaring everybody on the deck, and it was seriously frowned upon.
As I said Bagrat always got aboard. The weather didn't matter, the Dutch Roll didn't bother him, pitching deck no problem. He didn't have many wave-offs and didn't bolter very much.  I asked him about it one day and he told me that he learned how to get aboard with the Australian Navy. At that time the ship he was attached to didn't have an optical system and so pilots spotted the deck every trap. I can say that Bagrat wasn't one to tell stories so I will take him at his word here. So he was qualified for a time flying off Australian boats, and when I knew him he was qualified flying off the Nimitz class.
Oh, one more thing. Every squadron had what we called zappers. These were decals with the Squadron logo on it. They were usually ovals and around 4 inches on the long axis, and you could stick them on your cruise box, book, whatever. During a Mediterranean cruise a US pilot off one our carriers mistakenly landed aboard a French carrier we were war gaming with. If my memory serves me correctly it was the Clemenceau. After trapping aboard their ship, they zapped his aircraft with a whole lot of zappers, and gave him a complimentary cat shot back home. He should have gotten an honorary qualification, and I sure hope he logged it!

I don't recall any nation's outside the US operating hornets from a carrier.  But it used to be that the Argentine Navy who had a carrier and operated A-4s and Super Etendards would make practice traps and touch and gos on US flat tops which were on operations near the coast of Argentina when their carrier was out of action.  There are a few stills of this taking place, even in the 2000s, in the video below.

Was that during a UNITAS exercise?

It happen periodically when one of our carriers is in the area.

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text:
Do carrier-less militaries retain the equipment for carrier operations?
"How do jet fighters get to war?" made me wonder if aircraft used by the U.S. Navy and U.S. Marine Corps for carrier operations retain their carrier equipment when sold to foreign powers who do not operate carriers?
Pros would be the reduction in weight, repair/maintenance complexity, and cost (why bother paying for equipment you don't use?).
Cons would be engineering complexity (if they're not designed as optional components) or airworthiness (if the components have secondary functions beyond carrier operations).
The initial thought was prompted by a CATOBAR aircraft, but if something like the Harrier has different equipment, that would be relevant, too. What's the reality?

Another pro to removing the equipment would be be stocked up oin spare parts

The most common case is that the aircraft sold to non CATOBAR navies/air forces is built to a different configuration.
For example, the Canadian, Spanish, and Swiss F-18's were each sold under a different configuration.  Some of the weight penalties, maintenance and upkeep costs, and the substantial training costs to maintain CATOBAR currency and proficiency were not a concern and not needed.  This makes sense: since those flying services didn't have a carrier operations requirement, but they liked a variety of features that the Hornet provided (such as two engines).

Reasons for the selection listed by the Canadian Forces were many of
  its requested features were included for the U.S. Navy; two engines
  for reliability (considered essential for conducting Arctic
  sovereignty and over-the-water patrols), an excellent radar set, while
  being considerably more affordable than the F-14 and the F-15. The
  CF-18 was procured from 1982 to 1988, at a total capital cost of $4
  billion in 1982 dollars.

Interestingly, that early Canadian buy retained most of the CV features, and IIRC they were the first non US buyer of the aircraft. (Memory foggy on that one).

Export Hornets are typically similar to U.S. models of a similar
  manufacture date. Since none of the customers operate aircraft
  carriers, all export models have been sold without the automatic
  carrier landing system, and Royal Australian Air Force further removed
  the catapult attachment on the nose gear.[24]

For the non CATOBAR case, the current plan to deploy Marine F-35B's on Royal Navy carriers answers the rest of your question.

LONDON — The U.S. Marine Corps will deploy its Lockheed Martin F-35B
  Lightning II strike fighters on combat sorties from Britain’s new
  Queen Elizabeth-class aircraft carriers, a senior U.K. Royal Navy
  officer has confirmed.

@T.J.L.  Oops, thanks, got it.

Tthe QEs are STOVL carriers, and the F-35B is a STOVL fighter. So this is actually its intended use case. A dozen or two will also be sold to the Italian air force to operate from short runways, rather than STOVL carriers. I don't think they're changing any equipment though.

@HephaestusAetnaean What I have found in FMS is a variety of configuration differences that are subtle (Perhaps certain mission systems) and not a carbon copy.  As I don't have detailed info on the differences in F-35B (USMC) and F-35B (UK) I can't go any further. (I first encountered this with the USN Seahawk vs Australian Seahawk/S-70) and later in F-18 and F-16 configuration differences.


text:
How fuselage creates lifting force when plane flying on a side?
On a question "How plane able to fly on a side" people answer that it's because fuselage shape crate lifting force and plane should have enough thrust.
But that seems vague to me.
How fuselage creates lift ? Wing shaped that way that more air goes under it, so there more pressure below wing than above it. But fuselage is the same from both sides, so how it able to create lift after rotated on side ?

"Wing shaped that way that more air goes under it, so there more pressure below wing than above it." I do not think that is a good explanation of how a wing works.

@David K unexpected. And how do they work actually ?

You might try https://www.grc.nasa.gov/www/k-12/airplane/right2.html. They mention that even a flat plate can produce lift, although the pictures all show wing-shaped airfoils. There is plenty of discussion about the theory of lift in other questions on this site as well.

Has nothing to do with aircraft attitude. It has to do with the aircraft sideslip angle or yaw. If you stuff the rudder to one side, the aircraft is in a sideslip. The relative wind is now hitting the aircraft asymmetrically, from a direction to one side of the nose, and this creates a small amount of lift.

Wings and fuselages both produce lift in the same way: they change the direction of the oncoming air. If you want an object to generate lift, the object doesn't need to be any particular shape. You only need two things:

The object's cross section should be long and skinny.
The object should be at an angle relative to the oncoming air.

Fuselages are long and thin, and during knife-edge (sideways) flight, they're at an angle relative to the oncoming air. Therefore, they generate lift.
See also: How do symmetrical airfoils generate lift?

The photo that you posted already gives quite a few hints on how this can be possible:

The aircraft is flying at a sideslip angle (the nose pointed slightly up), so a part of the thrust vector is counteracting the weight.
It seems like the aircraft is not exactly perpendicular to the surface, so a part of the lift vector is still counteracting the weight.
The vertical stabilizers produce some "lift" in this situation due to the sideslip angle mentioned in 1. Note that these typically have symmetrical airfoils, so without the sideslip angle, these would not create any force.
The aircraft might be descending in a controlled way. In that case, not all of the weight must be carried.

As an example, look at the high sideslip angle here:

. There you can also see the rudder being deflected for trimming.

With proper attitude control and enough thrust, a washing machine or a refrigerator can fly. Angle of attack and lift are not something exclusive of wings...

Aircraft have multiple surfaces that move, in a maneuver like the one you posted a picture of, the aircraft will be relying on multiple surfaces to maintain altitude, this is a combination of the ailerons, the rudders, and elevators.
Objects in motion will stay in motion until they hit something.  Also, the forces of flight don't necessarily mean straight up and down, those axis's can move relative to the aircraft.
Source- Pilot for years.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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On a "Visual Approach", do I execute a "missed approach" or do I go around?
Let's say the weather is a little above VFR minimums (let's say it is 1700ft and 3SM).
The approach controller vectors me on to the final, and then clears me for a visual approach. For some reason (such as bad crosswinds), I feel like aborting my approach.
At this point, am I allowed to "go around" or do I have to execute a missed approach procedure (if so, which one?) unless advised otherwise by tower?
And what if it was an uncontrolled airport whereby I'd have to make this decision myself before contacting approach again?

First, a caution: IFR procedures can (and do) vary between countries. It is incumbent on the pilot to study the respective authority's Aeronautical Information Publication (AIP) to understand local procedures before flight. When asking questions about instrument flight procedures, it is helpful to know which countries you are specifically traveling through. While the vast majority of countries simply adopt ICAO procedures, many have significant deviations (the United States included).
ICAO Doc 4444 (PANS/ATM) section 6.5.3 discusses instrument flight that terminates into a visual approach. Interestingly, the document is silent on what happens if the approach is aborted.
In the United States, the FAA is more explicit. In the Aeronautical Information Manual, section 5-4-23 addresses visual approaches. Paragraph (f) details what should happen if a visual approach is terminated:

A visual approach is not an IAP and therefore has no missed approach segment. If a go-around is necessary for any reason, aircraft operating at controlled airports will be issued an appropriate clearance or instruction by the tower to enter the traffic pattern for landing or proceed as otherwise instructed. In either case, the pilot is responsible to maintain terrain and obstruction avoidance until reaching an ATC assigned altitude if issued, and ATC will provide approved separation or visual separation from other IFR aircraft. At uncontrolled airports, aircraft are expected to remain clear of clouds and complete a landing as soon as possible. If a landing cannot be accomplished, the aircraft is expected to remain clear of clouds and contact ATC as soon as possible for further clearance. Separation from other IFR aircraft will be maintained under these circumstances.

(This aligns with the FAA's guidance for controllers, JO 7110.65 7–4–1, which says that ATC is not required to assign an altitude because the pilot is expected to climb to pattern altitude.)

By the way, one of the reasons for requesting a visual or contact approach rather than cancelling IFR is that you are still in the system. In the event that you can’t land, you can be vectored by ATC and try again. You don’t need to remain VFR and request an IFR clearance like you would if you had cancelled.

@JScarry, I want to clarify that while you don't have to remain VFR in the literal sense, a visual approach is predicated upon the pilot having either the airport or a preceding identified aircraft in sight AND the airport must report a ceiling at or above 1,000 feet and visibility of 3 miles or greater (i.e. the airport must be VMC). A contact approach only requires 1 mile visibility. You MUST remain clear of clouds during either type of approach. If these conditions can't be satisfied, the pilot should use an instrument approach instead. See InFO 11003 (http://bit.ly/2vcWZjO)


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Aerodrome actual weather - METAR decode - 3 letters for this sky?
How can I describe this sky, in 3 letters as per the Aerodrome actual weather - METAR  decode?
I found online a comprehensive list of Metar codes

Looks like Broken (BKN) to me, but you also need to provide base altitude, so just BKN doesn't accurately describe the picture.

This work sheet may be of use and generally the system of Okta is used to denote coverage in a Metar, but I would say

L1 Clouds: Cumulus (Cu) with little vertical extent

but it could also be

L5 Clouds: Stratocumulus (Sc) not from spreading out of Cumulus (Cu)

But I will agree with Ron on this one, its BKN (5-6 Okta based on the picture in my opinion)

Looks scattered to me


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Conducting a Precision Approach on a Non-Precision Runway - What are my limitations?
Let's take ILS, for example.
As stated in the FARs, the minimum RVR for a CAT I ILS approach would be 2400ft (1/2 SM) for a runway that does not have TDZ and Centerline Lighting. So, that is one limitation for such a scenario.
A couple more would be the limitation to the visual references available under 91.175 of the FARs.
Can you think of any other disadvantages if one were to conduct a precision approach on a non-precision runway?

Your limitations are exactly the same regardless of runway -- you cannot descend below the published DH without the published flight visibility minimum and the visual references required by 91.175.
What the limited runway markings and lights change is the number of visual cues you have to be able to descend below MDA and land, which affects the likelihood of a successful approach in minimum weather.  Whether this is a disadvantage or not depends on the actual weather and your preparation.  If you know what lighting and markings are available (and you should), then you know what to look for.  If you are looking for lights that don't exist, you won't find them and worst case you may mis-identify other lights.
The only other disadvantages I can think of relate to ground movement and ILS critical area protection.  If there are no centerline lights on the runway there probably aren't lighted runway turnoff lead lines either and extra care needs to be taken when taxiing.  If the runway is located at an non-towered field and the ILS critical area has a hold short line on the taxi way, it may not be protected properly.  This is mitigated, however, by taxiway placement which probably avoids the critical area at non-towered fields (not universally true though).

So basically what you're saying is, if you can see X you may descend; if an airport doesn't have X you can't possibly see it, and if you do, you're at the wrong airport, or looking at the wrong thing/wrong lights? That actually makes a bunch of sense logically. :)

How often do non-towered airports have ILS? Or should I ask a new question...

@FreeMan http://aviation.stackexchange.com/questions/5163/do-non-towered-airports-commonly-have-ils and there is also the more common situation that the ILS is at a part time tower and they'll leave it on (for one of the runways) overnight when the tower is closed.

Thanks, @casey. Totally contradictory to the sense that's common in my head, but that's why I'm here - to learn.


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When is Class Delta Airspace not Class Delta?
Although there could be many examples, I'm using the KLCQ airport in this case. This is how the airspace stands:

In the CHART Supplement, it is mentioned that it's a "Class D svc other times class E".

I called the Airport Manager and he confirmed saying "Yes, we're a Class D during the time tower is in service. Other than that, it's Class E".
Questions:
1) Why does this airport not have a dashed blue circle like a normal Class D?
2) Since it's inside a Class E Transition airspace, shouldn't the airspace be Class G up to 700' AGL when tower is not in operation?
3) What is primarily required for an airport to actually be designated as a Class D airport - x amount of traffic, x amount services, x amount of weather reporting capabilities?
Why should this matter?

Weather minimums
Communications with ATC during arrival/departure
Etc.

Since you confirmed it is class D airspace it needs to have a blue dashed line.  If it goes to class E airspace it may also require a magenta dashed line.  Looks like you found an error.  Report it. There is a way to report discrepancies on the sectional chart informational tab.

I believe this is a duplicate of another question - Uncontrolled airspace around a towered airport.  http://aviation.stackexchange.com/questions/29823/can-an-aerodrome-in-class-g-airspace-be-controlled/29838#29838

I suspect the chart update is lagging behind the airspace changes there. See this answer for some related information.

Class D need a tower and alternate airport-approved weather reporting

I just pulled this airport up in ForeFlight and the blue dashed line is there, inside the magenta Class E boundary. So the charts have caught up with the change in airspace classification.

@wbeard52 -- just for the record-- (a bit late!) -- a dashed magenta line is not used in the depiction of airports that are Class D and revert to surface-level Class E when the tower is closed.  There is a dashed blue line, and a notation on the chart to "See Notams/Chart supplement for eff hrs Class D" or something to that effect.

@wbeard52 -- (ctd) --   A pilot seeing this notation on the VFR sectional chart-- at least in the case of an airport lacking any surface-level Class E extension, since airports with such extensions are treated slightly differently-- has no way to know without checking the Chart Supplement or other resources whether the airspace becomes G or surface-level Class E when the tower is closed.  There are many examples of each possibility.

@wbeard52 -- (ctd) --Re "has no way to know without checking the Chart Supplement or other resources" -- I'm considering submitting a suggestion for a new chart notation system that would change this situation.


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How do airlines plan their payload for multiple flights in a day?
Of course, this isn't specific to a single airline or airplane. As a base rule, it is needless to say that airlines want to profit as much as they can and the payload is a strong factor to influence the profits.
That said, let's take an example of a B737 of ABC Airlines that will be making stops to 3 different destinations before reaching its final destination.
Assuming 2 of the 4 legs have sold all seats, while the other 2 have sold only half:

How will the fuel on-board be planned? Will it benefit to carry enough for 2 legs so that they spend the least amount of time at the stop-over?
Will it benefit to only have the required fuel for one leg (including the reserves and alternate), and thence allow more luggage from passengers which would otherwise be declined?
Are these decisions made by dispatchers, pilots or a different department? Are they made right before each flight or pre-planned well in advanced?

I'm asking these because I want to understand how airlines plan their flights as to, you guessed it, maximize profits while still maintain inflation schedules and passenger satisfaction.

Layover time is determined by the scheduling of the flights. The ground crew may be able to turn the plane around in 35 minutes without adding fuel, and 45 minutes with a fill-up, but if the next leg isn't set to depart until 65 minutes after arrival (Note: all times made up for example purposes only), there's no time benefit to have carried the leg 2 fuel on leg 1.

In general - no. Unless fuel is very expensive at the arrival port, most airline generally don't 'tanker' ie. take fuel for the next flight. 2. No, passenger baggage is not the usual determinant in when to tanker, because it's predictable within a well-defined limit. 3. By dispatchers, if the rare situation occurs where they have to tanker.

The only real answer we can give to this is it depends
It depends on the airline, the nature of the legs (long/short), the specific airports/countries involved (re-fuelling costs can vary significantly) and route profiles used.
If the aircraft is doing 4 very short legs, the cost of carrying the fuel may be less than the cost of refuelling three times. Equally it's certainly faster to fill the plane once, rather than 1/4 fill it 4 times, because so much time is spent in setting up etc, and you can't usually re-fuel with passengers on board.
On the other hand, if legs 1 and 3 are nearly at the endurance of the aircraft, you physically can't carry fuel for legs 2 and 4: your fuel tanks aren't big enough. Equally on longer routes, the cost of carrying extra fuel increases dramatically.
Flip that around and say that legs 1 and 3 are short, but legs 2 and 4 are long (without being at the aircraft's endurance) and you have a problem that during legs 1 and 3 you're carrying a lot of un-neccessary fuel.
All airlines will have different policies and procedures, and those policies will vary wildly depending on the fuel costs at different airports. But I'll try to summarise at least some of the options here

For lots of short routes, fuelling once for multiple legs can be viable, but may not be the best option depending on fuel costs at each location. You wouldn't necessarily do a full day on one re-fuelling instance, but you may fuel twice for 4 legs, for example
For a short leg followed by a long one, it's rarer but the above will still reply
For a long leg followed by a short one, it's unlikely to be cost effective, although in certain situations your second leg's fuel load could be close to the reserve needed for the first leg: as long as you don't have to eat into your reserve on the first leg, you don't necessarily need to refuel.
For multiple long legs, you almost certainly don't have the fuel capacity, and carrying so much extra fuel for so long makes little sense: that's expensive.

In short, you usually want to fly with as little fuel as possible - a light aircraft is cheaper to run, can hold more cargo/luggage etc.
In a few situations, the cost of refuelling can make it worthwhile to fuel up in one location, where the cost of fuelling there makes up for the cost of carrying that extra fuel around. That's a niche scenario though, and wouldn't be the "usual" mode of operation for most airlines

In general, tankering (taking fuel for subsequent fllights) is pretty rare in first-world countries. For most airlines/schedules, you flight plan fuel for just that sector, and flight plan again uplifting fuel at the next port. For 3rd world ports, the situation can be different, but it's unusual. For long haul flights, it's irrelevant: you have to uplift fuel for the next sector at your destination port regardless.

Question number 3 is the only one that can be answered without involving too many unknown variables.
The final responsibility lies with the crew and particularly the commander or captain on a particular flight. The crew's job is to make sure that a) regulatory requirements are met and b) that commercial interests are considered, in that order. A third component is common sense, airmanship or whatever you want to call it, which aims to make sure that the mission is accomplished with a reasonable margin to minimum requirements.
The answer to question 1 and 2 depends on a range of factors:

Fuel price at the various ports of call (is fuel even available everywhere?).
Other fuel related restrictions at various airports. In some places passenger boarding is not allowed during fuelling, which slows down the whole process.
Weather conditions at each stop.
Landing and take off weight restrictions depending on runway conditions and performance requirements due to runway length or
terrain around the airport.
The cost of time vs fuel burn. How expensive is additional fuel burn in comparison with aircraft leasing costs, engine maintenance and crew salary? There might be cases where a set
of flights can't even be legally assigned to the same crew unless
they are completed within a certain time frame due to duty time
restrictions.

All of these factors lie mainly within the responsibilities of management and long term planning staff.
In practice this all works out so that a crew checks in for a duty and receives a plan for the flights of the day, including a suggested fuel figures and fuel strategy. The crew then accepts the plan as it is or makes required adjustments to it. Again, this procedure varies from airline to airline. In some airline the preparation work is done by designated staff, while other airlines might rely more on computer generated plans, which of course leaves a larger share of the responsibility with the crew.

So, in general, flight planning decide what fuel is required, and it usuallly results in fuel being loaded at each port on the trip. As always though, the captain has final discretion over those decisions and make his or her own decisions on fuel requirements.


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Would it be safer if Drones carried transponders?
The current FAA regulations don’t permit UAS above 400’ AGL, but that doesn’t mean that the machines are not capable of flying higher than that.
Since a Mode-C (at the minimum) transponder is required in various airspaces, is it a good time to start considering the fact Drones should start carrying some sort of altitude-reporting transponders?

In the world of drone operators, for every 1 that follows the regulations, there are like 10 who don't.

Should they all have ADS-B Out as well by Jan 1 2020, like most other aircraft will do, if flying in airspace where Radio Comm's are required?  These guys are making some pretty small units  https://uavionix.com/

The wording of the fact Drones should start carrying gives me the impression that your mind is already made up. If this isn't the case you might want to edit your question.

I'm sorry, but I can't see why this question would need to be reopened. What would make it not "opinion based"? How is "would it be safer?" not a call for opinions?

It is of course a good time to begin considering this, and in truth, it's already a consideration. It's also an assumption by many in the private sector that the FAA will mandate this for commercial drones. Recreational drones will not be allowed to fly at high altitudes any time in the near future, however, as companies that aim to autonomously transport clients with drones are starting to test their aircraft, it will be very necessary.
The difference between recreational drones and commercial drones is largely their operating space. A recreational drone pilot has no good reason to fly anywhere near 1000 feet, though the technology is becoming more easily available to do so. If you operate under the assumption that the majority of drones are likely to be under 1000 feet, you can somewhat rule them out as factors in commercial operations, for now. Recreational drones are also very small, and they are generally looked at as having similarities to bird strikes - the difference is, there are effective ways to get rid of drones, and not as many effective ways to get rid of birds!
Beyond the fact that commercial transport drones would be flying at higher altitudes, they would also be much larger, and could cause much more damage in an accident. ADS-B will no doubt be a requirement for commercial drones (perhaps of a certain size or above a certain altitude), in the near future. The FAA actually broached this topic with the industry at EAA this past summer.

Given how many drones are flying around today, equipping each with a mode C your mode S transponder  would be a nightmare for other pilots using ADS-B compliant traffic systems, and make it increasingly difficult for them to filter between non-issue traffic like a drone at 300 feet versus another aircraft flying up there altitude. I’ve done quite a bit of flying out in Southern California area in recent times, and we constantly get Drone NOTAMS all over the place.   It’s to the point that any kind of flying under 1000 feet AGL, the pilot needs to be a constant alert for such small unmanned aerial systems.   For those reasons, no I don’t think there’s ever going to be requirement issued to put transponders in drones.

You can typically filter out traffic between a particular altitude.


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Is it possible for ATC to see who’s transmitting on the radio on their radar?
I don’t think ATC currently has the capability of seeing who’s actually transmitting on the frequency.
If technology permits (probably by making a connection between the radios and the transponder), would it be helpful for controllers to be able to know the actual aircraft that’s transmitting on the frequency through their radar?
Does it also have the possibility of eliminating the requirement of saying the callsign after each transmission (might help in extremely busy airspaces)?
The visual aspect would be similar to how the “ident” feature works (like seeing a little “TX” when someone is transmitting).

There seem to be two questions here. The title asks whether it's possible, while the body says you don't think it's possible but asks whether it would be helpful.

This question also lacks a region or country- capability differs accordindly.

What real world problem is this going to solve?
If the callsign isn't used, how will those listeners without radar identify them? Radio communications is helpful for other aircraft maintain situational awareness.

A version of this has been implemented in some areas, such as the Maastricht Upper Area Control Centre, using radio direction finding equipment.
The EUROCONTROL website provides an explanation of the system, including an image of how it appears on radar displays:

Using triangulation software, the Radio Direction Finder, recently deployed throughout MUAC’s international airspace (the upper airspace of Belgium, the Netherlands, Luxembourg and north-west Germany) calculates accurately an aircraft’s position on the basis of its radio transmissions.
In densely occupied airspace, the Radio Direction Finder assists the controllers in rapidly identifying which aircraft is transmitting on the frequency.  This is particularly useful in MUAC’s sectors where controllers handle up to 25 aircraft at any one time, and is a prerequisite for the implementation of the free route airspace, planned at the end of the year. The origin of a voice transmission appears clearly on the controller’s integrated Human Machine Interface and is totally independent of conventional radar- and GPS-based aircraft localising techniques; this feature contributes to reducing call sign confusion, read-backs from wrong aircraft or crossed transmissions.

As you state correctly, they can’t see who is transmitting.
Despite that the functionality is not build into the radios currently installed in thousands of planes, that would also mean you would have to register a hand radio a specific plane.
In theory you could use analog technology to transmit short data pieces with every PTT. There is a good reason why aviation is still analog though. Analoge signals can still be understand, even if connection is really bad. It will be a lot more noisy and the pilot might not be understandable crystal clear, but the message will arrive. While in a digital environment you will get what you have on your mobile.
If you take bad connections in consideration, you would need to send the data signal several times to be correct and display the right call sign. That would probably take more time and block the frequency.

In amateur radio, and some other uses, there is CTCSS for, IIRC, Continuous Tone-Coded Squelch System. It uses low-frequency tones (below about 250 Hz) to allow a receiver to open the squelch only when a "valid" signal is being received. I don't think it sees much use outside FM, but I don't see why a similar system couldn't be used with AM. Reserve a couple of low-frequency tones and they could be notched out in the LF or AF stages without significantly impairing human understanding. From there, simple AFSK could be used to transmit short bursts of data such as a 24-bit mode-S transponder ID.

Mostly No, as normally configured. Slow traffic or particular positions may be identified by ATC listening on two radios simultaneously i. e. a BUEC, RCAG or portable radios especially, could identify how far away you are by precisely setting the squelch on a PET-2000 or other portable radio. The antennas for such facilities are at different locations which affects where transmitted signals will be received. It would be fairly easy with slow traffic and particular locations given multiple or lengthy transmissions.

Military transponders had, or possibly still have, a switch that, if selected, will cause an IDENT during every radio transmission. This would have been very useful on radar displays with no target datablocks.

This is true, at least up until 2006.  I can't remember the name of the switch position, (I never used it) but that is exactly what it did.

As David pointed out, they do not have any way to know where or who you are by com radio.
In the United States the FSS use to have directional steering capability for lost airplanes (and be able to locate the aircraft transmitting), but even that was done away with outside Alaska in 2007, then in Alaska in 2013. You would ask for a "directional steer" and they would ask estimated ground speed and would have you do a couple turns over a 3-5min period to identify your location by triangulation.

This is just wrong! Using VDF you can! Check Zachs answer

@pcfreakxx - Because this question lacks a region or country- capability differs accordingly. My answer is correct for the the United States (which it clearly stipulated). There is no longer VDF in the US.


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When is jet engine thrust maximum?
Assuming we have a convergent nozzle I've read that the maximum thrust is achieved just in the moment the nozzle exit -minimum area- is chocked, i.e., the nozzle is adapted in the sense the pressure in the exit area equals the ambient pressure. How can I demostrate this with formulas?

With a subsonic aircraft and a choked convergent nozzle, the gas pressure in the exhaust will be higher than ambient pressure. What exactly do you want to catch in equations? Thrust, efficiency, exhaust pressure?

Let's look at two cases, choked exhaust and complete expansion:
1. Choked exhaust
With a convergent exhaust pipe, the jet engine thrust reaches a maximum at the speed of sound of the exhaust gas stream.
The velocity of the gas flow increases if it was subsonic at the entrance of the pipe. In a convergent nozzle the maximum gas exhaust velocity is M = 1, the speed of sound at the temperature of the hot exhaust gas. With a choked exhaust, at M = 1 in the exhaust outlet, the static pressure is higher than ambient pressure.
The exhaust area needs to be reduced until the gas exit velocity is M = 1, which at for instance 800 ºC is 657 m/s. The pressure $p_e$ at the exhaust outlet will then be:
$$ p_e =\frac {\dot{m}\cdot R \cdot T_e}{V_e \cdot A_e }$$
which is greater than the ambient pressure $p_0$.
The net thrust $F$ of a pure jet engine is
$$ F = \dot{m} * (V_e - V_0) + A_e * (p_e - p_0)  $$
$R$ is the gas constant. Parameters you need to know:

outlet mass flow from the turbine $\dot{m}$ in kg/s
gas outlet temperature $T_e$ in ºK
speed of sound at $T_e$ in m/s, which for a choked exhaust is equal to $V_e$
outlet area $A_e$ in $m^2$
airspeed $V_0$ in $m/s$ and ambient pressure $p_0$ in $N/m^2$

If we use the following example of an aircraft flying M 0.85 at 30,000 ft, choked converging exhaust, exit area 0.1 $m^2$, mass flow 70 kg/s, exhaust temperature 1073 K, we get:
F = 70 * (657 - 258) + 0.1 * (328,106 - 30,100)
= 27,962 N from kinetic energy + 29,801 N from pressure difference, about the same amount.
2. Complete expansion
$p_e$ is now equal to $p_0$. This condition occurs if total pressure at the turbine exit $p_{Tt} \leq \epsilon_{kr} * p_0$, with $\epsilon_{kr}$ for a hot exhaust gas being around 1.95.
Analogous to the choked exhaust case:
$$ A_e =\frac {\dot{m}\cdot R \cdot T_e}{V_e \cdot p_e }$$
For the same conditions at 30,000 ft follows: $A_e$ = 1.09 $m^2$
and F = 70 * (657 - 258) = 27,962 N
The net thrust in this case is a lot lower because the turbine exit pressure is lower than in the choked case, and therefore the propulsive power of the jet engine is lower. Usually, in the case of a turbojet the turbine exhaust pressure $p_{Tt}$ is a lot higher than $\epsilon_{kr} * p_0$, which will lead to the choked exhaust case above.
Turbofans with a high bypass ratio have a low enough $p_{Tt}$ to allow complete expansion, most of the gas generator power being used for the bypass air compression.


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How much thrust is lost due to the bleed air system?
I've read that bleeding air for the pneumatic system from the engine core can produce important losses in thrust, and also rising the fuel consumption too. Today this problem is worse, with the more uses of high-bypass turbofans engines, which have less air passing through the engine core.
How much engine thrust is lost due to bleed air?

Are you asking about energy loss to bleed air in general, or only about energy loss to bleed air routed to pneumatic systems? Compressor bleed air is used for many purposes including bearing systems, engine cooling, engine control, pneumatic systems.

It's on the order of a few percent. Not huge but not negligible either.

This answer could be improved by providing more detail and sources.

It seems to be a more significant factor when one considers turboshaft powered aircraft. At least in the case of the old UH-60A Blackhawk helicopters which were (or are in the case of 1 remaining aircraft in the PR NG) powered by the GE T-700 engine. The activation of the engine inlet anti-ice, a bleed air pneumatic system, results in a loss of 16% available torque output. The UH-60L's GE T-701Cs addressed this issue but the mitigation only yielded a 2-3% available torque improvement. I suspect the greater realized loss of torque vs. thrust is explained by some insanely complex algorithm!


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What is the purpose of these "stickers" in the F/A-18 Super Hornet fuselage?

Photos source: screenshot from youtube video ->

I think they can be used as fuselage reference points in flight testing, but I'm not sure.
Are they part of NATO standard symbology?

These are definitely markers for some kind of tracking or video evaluation.

There's a big "STRIKE TEST" written on the sides of the fuselage, so I think your guess about reference points during flight testing is a likely situation.

That jet belongs to VX-23, which is a test and evaluation squadron from Pax River.

It may or may not be being used in this application, but they are location markers, usually used in weapons separation tests to record the movement and behavior of stores in the airstream as they separate from the jet.  Camera pods, usually mounted on the wingtips or other optimal vantage points record the process for engineering purposes.


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How can critical angle of attack of the wing of an an aircraft exceed even when the pitch angle is zero?
Normally one would expect that if the pitch angle is zero, that is the aircraft is level on the artificial horizon, how would the wing present itself to the relative wind at such high angle that it exceeds the critical AOA.?

What about descending vertically with the fuselage horizontal? Pitch angle = 0°, AoA = 90°. Descending vertically will obviously be in a stall condition.

But doesn't the vertical dive still provide lift in the horizontal direction (when wings push the aircraft along horizontally, parallel to the ground)?I thought pointing the nose down straight does not make aircraft go straight down.

In this case, the lift of the wings will make the aircraft going a bit rearwards  while going down, due to the small angle of the wings named c on this image (incidence angle), but the wings will be stalled anyway. You need to have a small pitch down angle to really have no thrust and fall vertically (well the aircraft will not stay in this position for a long time).

The suggested duplicate is worded in the opposite way, but the explanation is the same: pitch and angle of attack are two different, only loosely related quantities.

@user2927392: He's not describing a dive (nose pointed down) but rather falling-out-of-the-sky: the aircraft is falling but the nose is pointed towards the horizon. Imagine a child dropping a toy plane instead of throwing it. While that scenario sounds stupidly ridiculous something like it can happen in a flat spin.

That's one of the factors in the crash of QZ8501. They were confused about the stall warning while the plane was wings level. They weren't accounting for the effect of sink rate on the AOA.


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Is it possible to detect a pitot static failure (blockage) of air data probe during flight and alert the pilot?
Loss of static and pitot tubes affect the display of airspeed, altitude, vertical speed information. Loss of this information can  be catastrophic for flight. How are the pilots communicated about the failure of these ports (ex: when they get blocked). Or is there a system in place already that detects the blockage and unblocks it. Even if such system exists, what is done to ensure that pilot does not trust the airdata information displayed during the time when the ports are blocked?

Is there any redundancy maintained for these ports - like multiple static ports?

there are multiple pitot tubes.

Not a dupe, but reading the question should answer yours.

Even in presence of redundant systems, for instance if all the static/pitot tubes are temporarily blocked due to weather. I am assuming that there is a system that detects this and unblocks this (please correct if I am wrong). But is pilot notified about this so that he does not take any rash decision while the ports are being unblocked

For many aircraft, the pilot detects such faults by cross-checking the instruments and by analysis; in these aircraft there is no automated detection and alerting system for pitot/static system faults. Loss of such information should not be catastrophic, but would result in a partial panel emergency. For larger, more automated aircraft there may be automated fault detection and remediation systems.

The crew checks the pitots and static ports before the flight to ensure they are in good condition and not blocked by objects or insects. Pitot tube (pitot-static) can be obstructed in-flight. Static ports are less affected.
Detecting a blocked pitot or static port: This is not done, but is possible (e.g. send some air from the back of the tube in a pitot, and see if it can exit the tube at a normal rate (which is dependent on several parameters).
Unblock a blocked pitot: In some cases yes:

Melt ice or snow by heating the tube in flight, but the tube may be frozen for a minute from time to time. Some pitots are not heated and must be deiced naturally, which will be longer (while cruising in -50°C air, friction prevents aircraft skin to be cold. Concorde skin was about 100°C, meaning air friction just increased its temperature by 150°C).
Drain water using drain holes in the pitot.

Redundancy for pitots: Yes, two or three exist on most airliners.
Alert for blocked pitot: Not a direct alert, since a blocked pitot is not detected, but air data processors compare the different pressure values received from the different pitots, and in case of significant difference alert the crew and disconnect the automated units relying on pitot pressure (like the autopilot).
A message is displayed to emphasize that airspeed is unreliable
Dangerous? Yes because if the unreliability of airspeed is not taken into account by the pilot, then stress and inappropriate actions can occur because the aircraft is apparently not reacting to attitude changes.
AF447 disaster is sadly a perfect demonstration of the stress that can be generated.
If the crew detects correctly the situation, then there is nothing special to do, they just need to continue (manual control) at the same altitude and with the same aircraft attitude until the speed becomes reliable again.

Concorde probably isn't the best example to use for aircraft skin heating, though, being a supersonic aircraft. Traditional airliners have a dT (delta T, temperature difference) of closer to 25c (rather than the ~150c of Concorde), and their skin temperature can easily remain below 0 at cruise.

Loss of this information can be catastrophic for flight.

It is certainly a risk factor, but pilots have to do many mistakes before it really becomes catastrophic. There are procedures to get the plane safely to the ground even without that information.

How are the pilots communicated about the failure of these ports (ex: when they get blocked).

Failure of the ports specifically, rather than the system as a whole, can't be detected and if it can't be detected, it can't be communicated either. So it isn't.
Aircraft with three redundant systems and flight computer have the computer compare the readings and display appropriate message (airspeed disagree, altitude disagree, vertical speed disagree) and sound master warning if it detects mismatch larger than normal measurement error.
In smaller aircraft that don't have redundant pitot-static systems (light singles usually don't) and in older aircraft without flight computer it is up to the pilot(s) to spot the problem.

Or is there a system in place already that detects the blockage and unblocks it.

It is not possible to detect the blockage. The only unblocking mechanism is anti-ice, which simply heats the pitot tube to prevent ice buildup.
Only the pitot port, which faces forward, can be blocked in flight. The static ports face sideways and are almost impossible to get blocked in flight.

Even if such system exists, what is done to ensure that pilot does not trust the airdata information displayed during the time when the ports are blocked?

Nothing. Even if the system does detect a fault by comparing the values from the separate system, it does not know which of the systems is wrong. The pilots must decide themselves by combining other information they have and their understanding of physics of flight. They have pitch-power tables and other procedures to diagnose the problem.

Some planes are set up with triple redundancy (often found on Airbus planes)

(source)
In this case the system can reject the bad reading (caused by a blockage or bad probe etc.) by using the data from the 2 other sensors. The basic logic is that if all 3 probes are in agreement (same reading) they are all working. If at any given time one of the probes readings differs from two of the others then the reading is rejected. Of course this does open you up to the issue where two of the 3 probes fail and only a single probe is correct. However the chances of two probes failing and giving the same incorrect reading is low.
In modern planes things like GPS and INS units can be used to cross check the system but it will not necessarily be connected to all the same systems.
I don't know of any system that unblocks a pitot tube if a physical blockage is present, but if this is in reference to Air France 447, modern airplanes have a heater that can be applied to pitot tubes to de-ice them.

In general, unless there is a system in place to specifically detect this, pitot blockages are generally detected through erroneous readings on the instruments.  The good news is that most large jets have dual pitot static systems, one for the pilot’s displays and the other for the first officer’s.  Blocked pitot tubes can generally be spotted with unresponsiveness of the airspeed indicators or display tapes to throttle inputs while holding a level attitude or slower than normal displayed airspeeds at lower altitudes and faster than normal displayed airspeeds at altitudes higher than where the pitot tube became clogged.  A little experimentation and cross checking between the Captain’s and FO’s gauges can quickly determine the faulty system.

We have developed a prototype system we call 'Pitot Guardian' using proprietary hardware and software we can detect blockages and alert accordingly in order to ease the burden on the flight crew. The method we use does not interfere with existing systems and can detect problems before start up as well as in flight, preventing aborted take off roll if, at 'air speed active' the cross check shows an anomaly, and giving flight crews more time to make the correct decisions should icing overcome ports at altitude.

Welcome. Unless you are not authorized to disclose technical elements, it would be good to provide some explanations on the principle.

You may add links and references for further readings.

@ManuH only if actually further, the main answer should be here.


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How does pilot know when to trim when flying an aircraft that have fly by wire flight control computer
My understanding of trim (on non fly by wire aircrafts) is that when the pilot feels force on his column or side stick, he trims the aircraft (either up/down) until the forces on the stick or yoke are neutralized. But in fly by wire systems, the pilot does not feel any force on the stick or yoke. In such case how does pilot know when to trim the aircraft (be it pitch/roll/rudder trim).
Or does flight control computer computes the trim required automatically? In such case, what happens during the direct mode (or alternate law) when flight control computers are no longer in control and pilot commands directly go to actuator controller electronics.

The question you are referring talks about auto trim on FBW aircraft but my question is about manual trim

More generally, see How does trim work on an A320?

When the controls degrade to direct law the autotrim doesn't function. It puts a warning on the display to tell you autotrim is deactivated. That is what happened on XL Airways flight 888. The AoA sensors failed and the control law degraded. The pilot apparently did not realize the need for manual trim, lost elevator authority and stalled.

@mins the last two paragraphs in this answer to the second linked question seem to address how trim works without force feedback.

Fly-by-wire just means that the control column is not connected to the control surfaces (hydro-)mechanically, but using digital (electrical or optical) signal wires. That says nothing about how the controls behave. There are two basic ways they can:

The Boeing way:
Force and position is transmitted in both directions, emulating
control with mechanical link. The pilot feels force on the control surfaces and trims as usual.
The Airbus way:
The position of the control column corresponds to wing loading in pitch and roll rate in roll axis. The computer manipulates the controls to achieve the target values. The control column is spring-loaded, so force always corresponds to position.
The trim is operated by the computer to balance the control surface for wing loading of 1 G (or is not a separate control at all as in case of FBW fighters with all moving stabilator).
But when the system is in direct law (during take-off or if degraded due to fault), the trim still works more or less normally. The centred position of control stick corresponds to the trimmed position of the control surface, so if the pilot feels force on the control stick, because it is displaced, they dial trim and reduce pressure on the stick until the plane flies straight with the stick centred.

The Airbus way is used on Airbus A320 and all newer models, Sukhoi Su100 and some fighters (since F16).
The Boeing way is used on Boeing 777, 787 and, IIRC, some regional jets.

I suppose Dassault Falcon's way is similar to the airbus way. Do you have any further readings for this "airbus way"?

@ManuH, wikipedia has quite a lot of details already. There is also some pretty detailed document at smartcockpit (look for document named "Fight Controls").

I was thinking of decision process behind autotrim (subquestions of this question)

@ManuH, From pilot's point of view, the aircraft is always perfectly trimmed for straight flight path under autotrim. But I've never found a single word about when the ELAC actually decides to move the stabilizer (though in the plane it can be observed, because the trim wheels have hydromechanical link and turn when the stabilizer moves). Probably it's considered an implementation detail nobody needs to know.

Fly by wire isn't just that the signal is sent by wire, but is also interpreted and modified (mostly restricted) by a computer (either analog or digital)

@ChrisV, Fly-by-wire means digital signal, yes. That can still behave in any way the designers happened to think makes sense.

@JanHudec If you never heard when and how the ELAC decides to move the stabilizer for Airbus, maybe you have heard for other manufacturer's implementation (Dassault falcon 7X, Sukhoi Su100, ....)

@ManuH, of other manufacturers I didn't even look. For Airbus I did. But it is really implementation detail and as such will probably only be described in some internal documents. From point of view of pilots, the trim wheel is a funny widget that sometimes spins on its own that they have to know what it does in case the flight computers fail, but don't ever have to care about otherwise.


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How are helicopters's avionics powered during power-off autorotation?
Avionics such as an altimeter or a radio require electric power to work. The engine usually provides this power. How is this electric power supplied in case of engine failure?
I can think of the following solutions:

Batteries
APU
Using the shaft to turn an electric turbine (this could generate some unwanted torque)
Expecting the pilot to do without

What is the most common solution? Does it depend on the size or application of the helicopter?

Autorotation will only last a few seconds, so batteries will certainly power for the radios. The altimeter and many other instruments will be passive, if they are steam gauge dials.

FYI: Altimeters that work entirely from static air pressure are still very common today.  Many GA aircraft only have these, many aircraft with glass cockpits have them as an emergency backup.

Some helicopters will likely have standby instruments with their own backup power

On smaller rotorcraft the electrical generator can be a starter-generator, also used as a starter. On larger rotorcraft an independent alternator is usually installed on each engine. On largest rotorcraft, like CH-47, an APU is present, but is used only on the ground.
Generators/alternators are driven by an engine shaft, not by a rotor shaft, to supply electricity when the engine works, even when the rotor is still stationary, isolated by the clutch(es).
In case of all-engines failure, the only source of electricity for autorotation is the battery.
On a single-engine Bell 407:

With generator OFF, a fully charged battery will provide approximately 21 minutes of power for basic helicopter and one VHF COMM radio (35 minutes with optional 28 ampere/hour battery).

Source: Bell 407 Flight Manual.
The battery capacity allows a normal autorotation landing, which cannot last more than a few minutes. The longest descent would be from the service ceiling. Rough calculation:

Starting at the ceiling of 20 000ft,
with a maximum glide distance of 14 NM,
with a minimum speed of 55 KIAS,

the glide cannot last more than about 15 minutes (the longest helicopter autorotation is likely 30 minutes, from an altitude of 40 200 ft).

On small rotorcraft the electrical generator is reversible and is also used as a starter...  Not necessarily.  Rotorway, for example, (a kit-built 2-seater) uses a modified automotive engine with a normal automotive starter and alternator (and a bunch of other parts too).  You can even get them from car parts stores and use them as-is, if you know what cars originally used them.  (you can do that with experimental)

did they really write ampere/hour instead of amperehour battery in that source?!?... Addidionally: 15min in autorotation glide, wow! That would have to feel like an eternety to the pilot!

@kruemi: They did, common mistake but unexpected in a manual. The record for autorotation is about 30 minutes, when Jean Boulet reached the altitude of 40 800 ft in a Lama and the engine flamed out (many components had been removed to save weight, including the starter and the battery immediately after the engine had been started)


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Could Swashplate be replaced with small electric motors?
In helicopters, the swashplate is used to control the pitch of the blades. Could a set of electric motors, each placed at the root of each blade, be used to control the pitch instead? Has this method ever been attempted? What potential problems might arise?
Advantages I can think of:

Fewer parts
Ability to create more complex pitch curves
Lower complexity, especially for coaxial rotors

Are there any major problems with this approach that I might not be aware of?

This question is similar to: In helicopters, why not have electric motors controlling blade pitch?. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.

Yes that is possible and has been attempted by the german company Airbus Helicopter Technik GmbH (formerly called ZF Luftfahrttechnik GmbH) in cooperation with Sikorsky. They have published two papers (here and here).

The resulting rotor is quite a beast; note that the silver dome in the picture below houses all of the power electronics, which emit quite a bit of heat.

The advantages of installing this system are coupled to the IBC (Individual Blade Control) concept. Hereby, one can actuate each blade individually. This brings a couple of possible benefits

Reduction of noise, as one can prepitch the blade before beating through another vortex
Reduction of vibrations, by actively countering these (which is why this setup is interesting for Sikorsky)
Lower main rotor power demand, as less energy is wasted
(However not all of these benefits can be achieved simultaneously)

Obviously the system is quite complex, you need a lot of electronic hardware to manage the powerflow and this hardware has to be mounted on the rotorsystem. Especially interesting is the fact that the actuators are able to regenerate power as the blade is back-driven in some portions of its revolution. Distributing this power to the other actuators is a demanding task from an electronic point of view (something which a swashplate does for free).

But the gains might outweight this drawback especially for rigid rotor systems such as the Sikorsky X2 rotorsystem, as these rotors are naturally very prone to vibrations.
The authors claim that this system has been successfully tested on a teststand, but not yet in real-life. However, from personal experience I can say that the prototype is quite impressive.

To be fair, that is one location where cooling your electronics is NOT going to a difficult task!

@MikeB that's not exactly true. The exterior of the device is going to be in a relatively high airflow environment, but air cooling wont be optimal and that smooth dome is going to see radiation heating from the sun in addition to heat dissipation from the electronics. As this is on the rotor head so attaching cooling fins will be complicated by drag depending on how they are orientated. which might have flight characteristics issues. direct air cooling is difficult because air is an effective insulator.

In the paper, the authors state that at first they considered water-cooling the electronics, but opted to simply space out the electronic boards as much as possible to mitigate the problem. Looks like they were successful. But I agree, that convective cooling of the plate should provide ample cooling power if the helicopter is in free flight.

This is certainly possible, and as you wrote, would enable more complex control strategies, and with sophisticated programming would make controlling a helicopter much easier.
However, I dare say the system suggested by you is more complex than the current mechanical/hydraulic swashplate arrangement, adding possible points of failure, and to maintain safety, a lot of cost.
The system would need to consist of multiple components per rotor for redundancy, also the electric system of the helicopter would need to be upgraded to a more fail safe configuration. Also the control logic would not be a simple task to program, and again depending on application, double or triple redundancy would be needed for control computing.

Isn't a swashplate a complex system with lots of single points of failure as well?

@Michael but failures in an electronic system would likely be sudden and catastrophic, whereas in a swashplate they would more typically announce themselves via excessive vibration, sticky controls, loss of hydraulic pressure etc. before actually becoming bad enough to cause a crash. Redundancy can help to some extend in the electronic case, but it incurs a lot of complexity and failure opportunity of its own (you need to ensure the systems don't "fight each other").

@Michael It would seem so, but being (mostly) mechanical, the engineering behind the swashplate design is relatively simple and very much proven. This is entirely not the case with electronics, and certainly not with programming

The closest we should get to that is Fly-By-Wire helicopters, those have swashplates too but don't directly connect the controls to that.

Motors can and will fail more than mechanical links, and especially in places like the rotor of a helicopter, you really need to make sure everything is working fine and it's ok to have "more" parts.
Cost and complexity will probably also increase, since you have to maintain these motors which I think would cost more than the mechanical links. Complexity is created with all the associated systems that would be required for this. Complexity is reduced in one area but increase in a much worse way in other places.
In case of a failure I think these would be worse. Ensuring power supply to the motors in all scenarios will be difficult.

Really speaking there's not really a need to integrate motors there and swashplates are just fine.

There's lots of ways this can be done, and I'd highlight https://hackaday.com/2020/06/25/building-and-flying-a-helicopter-with-a-virtual-swashplate/ which simplifies the mechanical side about as far as it could conceivably go.
The big questions are reliability and failure modes: a swashplate allows autorotation in the case of powerplant failure, any alternative which relied on a motor to hold blade pitch at any particular point and didn't automatically revert to the neutral position on failure would be unsafe.


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Why are round nose cones more aerodynamical than pointy
I am wondering why round nose cones are aerodynamical than pointy nose cones. Lets say that the air is flowing exactly perpendicular to the pointy nose cone, why is the round one still better than the pointy. Lets also assume that the oncoming air is traveling at a subsonic speed. One theory I have is that air is flowing faster around the pointy nose cone and therefore the pressure is lower on the surface and then that causes more drag than the round. I dont know if that is correct or If there is another explanation. Could someone who knows this explain it?

Does this answer your question?

Good find, Wyatt!  Peter's answer suggests that a pointy nose is draggier when flow isn't axial, and says that a rounded nose suffers less from this.  Is that enough of an answer to "more aerodynamical" (less drag)?

@CamilleGoudeseune Thanks! I’m not sure if a round nose is more aerodynamic. The linked answer doesn’t mention that, and it wouldn’t really make sense. So, I’d say the only way a rounded nose would be more aerodynamic is when flow isn’t axial. In that case yes, I’d say that’s the best way to answer this.


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Are there any authority references showing how to track TSO/CSO?
The airlines that I worked for and I worked with has been tracking TSO value as same as TSN until the unit has been overhauled.
As far as I know this is the common practice and there should be some documentation,I couldn’t find so far. Do you guys know any reference for this or similar showing how to track serialised parts? Thanks a lot.


text:
how does a Sear Haack body and rotation interact
If a Sear Haack body is launched out at supersonic speeds and given a extremely high rotational speed will the Sear Haack body stay stable over a long distance or will it start to tumble and if it does fly with stability how dramatically is it affected by side winds. And does rotation effect the aerodynamics of the Sear Haack body in any way shape or form.

Quarterbacks in football may know the answer.

Well, all quarterbacks which throw at supersonic speeds that is...

OK, how about a rifle bullet


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What does this statement about steep descent mean?
Source: Wolfgang Langewiesche - Stick and Rudder; An Explanation of the Art of Flying
In the first chapter the author mentions, in a glide, if you want to descend more steeply, you want to want to point your nose less steeply.
And if you want descend less steeply you point your nose more steeply.
What is the reason for this?

The answer to this question might help clear things up

This one is about climb rates but it has a similar relationship

@mins This is just a second para of the book

Here's the question I was taking for. It should explain the concept,

Best angle of descent is in a spin.

The statement is only true if you fly at a speed below the best glide speed. For simplicity, let's look at a glider: Below you see the plot of the L/D ratio over speed of the DG-1000 two-seater glider:

Glide ratio over speed diagram for three different wing loadings (source). If we just look at the lowest wing loading (leftmost curve), the best L/D can be achieved when flying at 95 km/h. Minimum speed is around 62 km/h, so it is entirely possible to fly along at 80 km/h. When the pilot reduces the angle of attack, the aircraft will pitch down and speed up. If it now flies at 90 km/h, he has just improved his L/D from 43 to 46, so he will descend less steeply when dropping the nose.
Note that our flight path angle is now less steep, and the change in attitude is less than the commanded change in angle of attack. Nevertheless, the pitch attitude is reduced and the pilot has the impression that he dropped the nose.
The same is true in reverse when slowing down. When approaching the stall speed, large angle of attack changes will result in relatively small speed changes, so the effect of a steeper descent when pitching up becomes more pronounced as the airplane slows down.
The underlying reason is the fact that drag will increase when the pilot moves away from the best L/D speed. Slowing down will increase drag, and more drag will result in a steeper descent. As soon as he shifts his starting point to higher speeds, things reverse and the aircraft will descend more steeply when the nose is lowered.
Adding an engine will not fundamentally change this behavior. It is only easier to explain when using gliders.

That comment by Wolfgang Langewiesche in his book "Stick and Rudder" has caused lots of discussion over the years. Maybe that is what he intended when he worded it so ambiguously.

"By pointing the nose down less steeply, you descend more steeply. By pointing the nose down more steeply, you can glide further"

This is really only true if you are flying just a little bit slower than best glide speed (best Lift /Drag ratio) or (best glide distance).  Also, that statement is really only true if you point the nose up or down just a little.
Best glide distance means the speed at which the most distance is traveled for the least amount of sink. If you are flying slower than the best glide speed, putting the nose down and going faster, so that you are closer to the best glide speed, will allow you to cover more distance as the aircraft sinks.
If you are already flying at the best glide speed and point the nose down, you will no longer be at the beast lift to drag ratio. You will increase the speed and distance traveled, but you will also increase the sink rate and drag from the higher airspeed. That will result in a steeper descent because you are no longer at the best lift to drag ratio.
If you point the nose down to 60 degrees below the horizon I guarantee you will descend more steeply not less steeply and NOT glide farther as Langewiesche says in the book.

I spent past few days thinking over and over about this comment. I could not figure out how pointing nose steeply reduces the rate of descent. The potential energy that got converted into kinetic should only increase rate of descent.

@user2927392 It isn't about rate of descent, it is about the angle  of descent.

@user2927392 To expand a bit on Lnafziger's comment, the point is not that you're descending slower, but that you're speeding up and, therefore, covering more ground horizontally for the same vertical descent.

The key thing here is that he is referring to the ANGLE of descent, not the RATE of descent.
If you push the stick forwards the rate of descent will always increase, but the angle of descent may actually decrease. This is because you go faster so you generate more lift, thus your overall angle of descent will decrease.
A typical beginner's mistake some glider pilots make is that they get worried they are not descending fast enough when they are landing so they push the stick forwards to dive--a big mistake. What happens is they go a lot faster, so they tend to overshoot even more. Pulling back on the stick, slowing the aircraft down and flattening the pitch is what to do to steepen the angle of descent, just as Langewiesche says.

I would agree that diving is a big mistake, but slowing down is not a good idea either if it takes the pilot below the pre-determined safe approach speed for the conditions.  Especially so just before turning base/final.  Otherwise they could come down much faster than anticipated. :)

@webdevduck Obviously. Personally, I have never heard of a single instance where a student stalled and crashed a glider while in level flight on final. I realize some instructors have a paranoia this could happen, which is in my opinion completely unwarranted.

This is apparently talking about maneuver around the best glide speed. The behavior of an airplane is counter-intuitive then.
Pushing the nose down, increases the speed and causes the angle of descent to decrease.
Pulling the nose up, decreases the speed and causes the angle of descent to increase.

Whilst this might answer the question superficially, it would be much better if you could explain why so that the OP, and others coming in the future, can understand what happens.